1. Field Of The Invention
The present invention generally relates to information storage apparatuses and methods for storing data, and more particularly to an information storage apparatus and a method for storing data in which tracking error signals are generated by the differential push-pull method so as to control tracking.
2. Description Of The Related Art
In an information storage apparatus such as an optical disk device, it is preferable to perform a precise tracking operation in order to write and read data on a preformed track. One of conventional tracking methods is a tracking servo method that employs the differential push-pull method using a main beam and two sub-beams for generating a tracking error signal.
FIG. 1 shows a diagram illustrating an optical system employing the differential push-pull method.
Generally, in the differential push-pull method, a main beam, the first side beam preceding the main beam and the second side beam following the main beam are emitted onto an optical disk.
For example, such an optical system as shown in FIG. 1 can realize the differential push-pull method.
A laser beam emitted by a laser 1 is collimated by a collimator lens 2 and is split into three parallel beams by a diffraction grating 3. The three split beams are supplied to an objective lens 5 through a beam splitter 4.
The objective lens 5 condenses each of these three beams and focuses them on the optical disk 6. These three beams correspond to the main beam MB, the first side beam SB1, and the second side beam SB2.
The three beams are reflected at three spots on the optical disk 6 and are diverted to a condensing lens 7 by the beam splitter 4. The diverted beams, the first side beam, the main beam and the second side beam, are condensed by the condensing lens 7 and supplied to corresponding detectors 8a, 8b and 8c, respectively.
From three signals detected by the detectors 8a, 8b and 8c, three differential signals of the main beam, the first side beam and the second beam are obtained by a detecting circuit so as to generate three tracking signals.
FIG. 2 shows a block diagram illustrating a detecting circuit based on the differential push-pull method.
The detector 8a, which detects a reflected beam of the first side beam SB1, has two segmented detecting areas E2 and F2. The detector 8b, which detects a reflected beam of the main beam MB, has two segmented detecting areas E1 and F1. The detector 8c, which detects a reflected beam of the second side beam SB2, has two segmented detecting areas E3 and F3.
The detecting area E2 of the detector 8a is connected to a non-inverting input terminal of a differential amplifier 9a and the detecting area F2 of the detector 8a is connected to an inverting input terminal of the differential amplifier 9a. The differential amplifier 9a generates a tracking error signal TE2 corresponding to the difference between two signals from the detecting areas E2 and F2. That is, the tracking error signal TE2 corresponds to a tracking spot of the first side beam SB1.
The detecting area E1 of the detector 8b is connected to a non-inverting input terminal of a differential amplifier 9b and the detecting area F1 of the detector 8b is connected to an inverting input terminal of the differential amplifier 9b. The differential amplifier 9b generates a tracking error signal TE1 corresponding to the difference between two signals from the detecting areas E1 and F1. That is, the tracking error signal TE1 corresponds to a tracking spot of the main beam MB.
The detecting area E3 of the detector 8c is connected to a non-inverting input terminal of a differential amplifier 9c and the detecting area F3 of the detector 8c is connected to an inverting input terminal of the differential amplifier 9c. The differential amplifier 9c generates a tracking error signal TE3 corresponding to the difference between two signals from the detecting areas E3 and F3. That is, the tracking error signal TE3 corresponds to a tracking spot of the second side beam SB2.
The tracking error signal TE2 generated by the differential amplifier 9a and the tracking error signal TE3 generated by the differential amplifier 9c are supplied to an adder 10 that generates an added tracking error signal, which is the result of adding (TE2+TE3) the tracking error signals TE2 and TE3. The added tracking error signal (TE2+TE3) from the adder 10 is supplied to an inverting input terminal of a differential amplifier 11.
The signal generated by the differential amplifier 9b, that is, the tracking error signal TE1 of the main beam MB, is supplied to a non-inverting input terminal of the differential amplifier 11. The differential amplifier 11 generates another tracking error signal, which is a signal {TE1xe2x88x92(TE2+TE3)}, by subtracting the added tracking error signal (TE2+TE3) from the tracking error signal TE1.
As mentioned above, the final tracking error signal is generated by applying the differential push-pull method to the main beam and also the first and the second side beams. It should be noted that the same offset, which is caused by objective lens shift or radial skew, occurs in the original three tracking error signals TE1, TE2 and TE3 for the main beam MB, the first side beam SB1 and the second side beam SB2 because the same objective lens 5 is used. Thus, the final tracking error is without the offset caused by objective lens shift or radial skew.
Referring to FIG. 2, a spot 10b focused on by the main beam MB is positioned on a track TR0, a spot 10a focused on by the first beam SB1 is positioned on a guard band GB10 that is not used except as a space between the track TR0 and a track TR1, and a spot 10c focused on by the second beam SB2 is positioned on a guard band GB20 that is not used except as a space between the track TR0 and a track TR2.
In a conventional tracking servo method employing the above-mentioned differential push-pull method, it is assumed that the optical system in FIG. 1 operates on recorded tracks on which many pits P are formed on tracks TR0, TR1 and TR2. In this case, reflectance of the spot 10a nearly equals reflectance of the spot 10c because both spots 10a and 10c include parts of pits. Accordingly, there is no unbalance between two reflected beams from the spots 10a and 10c so that the offset caused by objective lens shift or radial skew is eliminated.
However, the conventional tracking servo method has a disadvantage that will now be explained.
FIG. 3 shows a diagram illustrating a case of causing an offset that should be eliminated.
Referring to FIG. 3, it is assumed that the optical system in FIG. 1 is operating around a boundary between a recorded area and a blank area. That is, the first side beam SB1 focuses on a spot 11a on the guard band GB10 in the blank area in which there is no pit and the second side beam SB2 focuses on a spot 11c on the guard band GB20 in the recorded area in which there are many pits P. Accordingly, the presence of a pit P in the spots 11a and 11c affects both reflectances of the first side beam SB1 and the second side beam SB2. Thus, unbalance between the reflectances occurs. Although the unbalance does not cause an offset directly, the offset can not be eliminated when objective lens shift or radial skew occurs simultaneously. In practice, the optical disk 6 is not flat and is not always mounted rigidly parallel to the focal plane.
Disadvantageously, a center of a peak value and a bottom value of a tracking error signal including the offset does not indicate a center of a track. Hence, data is recorded away from the center of the track because a tracking servo adjusts tracking by the offset so that a de-tracking is caused.
It is a general object of the present invention to provide an information storage apparatus and a method for storing data in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an information storage apparatus and a method for storing data which apparatus and method are capable of suppressing offsets of tracking error signals by a median of a peak value and a bottom value of a tracking error signal being obtained and data being recorded in accordance with the median especially in a case of operating around a boundary between a recorded area and a blank area.
The above objects of the present invention are achieved by an information storage apparatus generating a tracking error signal in which apparatus the differential push-pull method is applied to a three spot method using a main beam and two sub-beams, the main beam for writing data on a recording medium and reading data from the recording medium, the information storage apparatus including: a beam moving part moving the main beam from a blank track to a recorded track; and a center value calculating part calculating a center value of the tracking error signal when the main beam is moved from the blank track to the recorded track so that a reference value of the tracking error signal is corrected in accordance with the center value when the main beam writes data on the recording medium.
According to the present invention, it is possible to correct the tracking error signal generated around the boundary between the blank track and the recorded track in accordance with the center value. Therefore, an offset caused by the tracking error signal can be eliminated, which results in prevention of data from being recording off-track.
The center value calculating part according to the present invention may detect a peak value and a bottom value of the tracking error signal generated when the main beam is moved by the beam moving part, and calculate a median between the peak value and the bottom value so that the median is defined as the center value of the tracking error signal.
According to the present invention, the median calculated from the tracking error signal is set as the center value of the tracking error signal so as to correct the tracking error signal. Therefore, an offset caused by the tracking error signal can be eliminated.
Alternately, the center value calculating part according to the present invention may obtain a predetermined number of medians by the beam moving part operating the main beam at predetermined times and a median between a peak value and a bottom value of the tracking error signal being calculated every time the beam moving part operates the main beam so that an average of the medians is defined as the center value of the tracking error signal.
According to the present invention, the average of medians is defined as a center value of the tracking error signal. Therefore, it is possible to more accurately correct the tracking error signal in accordance with the center value so that an offset caused by the tracking error signal can be eliminated and it is possible to prevent a tracking servo from erroneously adjusting a position on a track by the offset.
The beam moving part according to the present invention is executed by a still regenerative command that operates the main beam to read data recorded on the recording medium and regenerate the data.
Moreover, the above objects of the present invention are achieved by a method for storing data in accordance with a tracking error signal in which method the differential push-pull method is applied to a three spot method using a main beam and two sub-beams, the main beam for writing data on a recording medium and reading data from the recording medium, the method comprising the steps of: (a) moving a main beam from a blank track to a recorded track; (b) calculating a center value of the tracking error signal generated when the main beam is moved from the blank track to the recorded track in the step (a); and (c) correcting a reference value of the tracking error signal in accordance with the center value when the main beam writes data on the recording medium.
According to the present invention, it is possible to correct the tracking error signal generated around the boundary between the blank track and the recorded track in accordance with the center value. Therefore, an offset caused by the tracking error signal can be eliminated, which results in prevention of data from being recorded off-track.
The step (b) according to the present invention may include the steps of: (d) detecting a peak value and a bottom value of the tracking error signal; (e) calculating a median between the peak value and the bottom value detected in the step (d); and (f) defining the median as the center value of the tracking error signal so as to correct the tracking error signal.
According to the present invention, the median calculated from the tracking error signal is set as the center value of the tracking error signal so as to correct the tracking error signal. Therefore, an offset caused by the tracking error signal can be eliminated.
Alternately, the step (b) according to the present invention may include the steps of: obtaining a predetermined number of medians by the step (a) being performed at predetermined times and a median between a peak value and a bottom value of a tracking error signal being calculated every time the step (a) is performed; and defining an average of the medians as the center value of the tracking error signal so as to correct the tracking error signal.
According to the present invention, the average of medians is defined as a center value of the tracking error signal. Therefore, it is possible to more accurately correct the tracking error signal in accordance with the center value so that an offset caused by the tracking error signal can be eliminated and it is possible to prevent a tracking servo from erroneously adjusting a position on a track by the offset.